Directed Motion of Metallodielectric Particles by Contact Charge Electrophoresis

We
investigate the dynamics of metallodielectric Janus particles
moving via contact charge electrophoresis (CCEP) between two parallel
electrodes. CCEP uses a constant voltage to repeatedly charge and
actuate conductive particles within a dielectric fluid, resulting
in rapid oscillatory motion between the electrodes. In addition to
particle oscillations, we find that micrometer-scale Janus particles
move perpendicular to the field at high speeds (up to 600 μm/s)
and over large distances. We characterize particle motions and propose
a mechanism based on the rotation-induced translation of the particle
following charge transfer at the electrode surface. The propulsion
mechanism is supported both by experiments with fluorescent particles
that reveal their rotational motions and by simulations of CCEP dynamics
that capture the relevant electrostatics and hydrodynamics. We also
show that interactions among multiple particles can lead to repulsion,
attraction, and/or cooperative motions depending on the position and
phase of the respective particle oscillators. Our results demonstrate
how particle asymmetries can be used to direct the motions of active
colloids powered by CCEP.